Just a bit more information about the strain gauges used in loadcells. The basic strain gauge found in nearly all cells is a bridge of 4 resistors, these resistors are wired as a whetstone bridge. This bridge needs to be read by an ADC with a differential input. The strain gauge is "excited" by a voltage typically between 1V and 10V, the gauges produce very small signals, normally a gauge may be specified as 2mV/V, this means for an excitation voltage of 1V it will produce 2mV output at maximum load. Similarly for an excitation of 2.5V it would produce a full scale output of 2mV * 2.5 = 5mV. As you can see the voltages involved are very small hence the need for an ADC with amplification like the unit mentioned above from ebay (I've not tried this but it looks to be made to read loadcells).
Another thing not note is that your accuracy depends on the stability and accuracy of your excitation voltage, so this is generally fed from a voltage reference.
Hope the above helps
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